Sources

Christopher Upward & George Davidson, The History of English Spelling (2001)http://www.historyofenglishspelling.info/David Sacks, Letter Perfect (2003)Kevin Stroud, The History of the Alphabet (audiobook)David Crystal, The Cambridge Encyclopedia of the English Language (2003)A. Campbell, Old English Grammar (1991)Raymond Hickey, “On the nature of the labial velar shift”, Journal of Phonetics 12 (1984): 345-354.NativLang “Thoth’s Pill - an Animated History of Writing”